Rapid advances are occurring in various electronic devices especially display devices that are used for various communicational, financial, and archival purposes. For such uses as touch screen panels, electrochromic devices, light-emitting diodes, field-effect transistors, and liquid-crystal displays, electrically-conductive films are essential and considerable efforts are being made in the industry to improve the properties of those electrically-conductive films and particularly to improve metal grid or line conductivity and to provide as much correspondence between mask design with resulting user metal patterns.
Electrically-conductive articles used in various electronic devices including touch screens in electronic, optical, sensory, and diagnostic devices including but not limited to telephones, computing devices, and other display devices have been designed to respond to touch by a human fingertip or mechanical stylus.
There is a particular need to provide touch screen displays and devices that contain improved electrically-conductive film elements. Currently, touch screen displays use Indium Tin Oxide (ITO) coatings to create arrays of capacitive areas used to distinguish multiple points of contacts. ITO coatings have significant disadvantages and efforts are being made to replace their use in various electronic devices.
Silver is an ideal conductor having an electrical conductivity 50 to 100 times greater than ITO and is being explored for this purpose. Unlike most metal oxides, silver oxide is still reasonably conductive and this reduces the problem of making reliable electrical connections. Silver is used in many commercial applications and is available from numerous sources. It is highly desirable to make electrically-conductive film elements using silver as the source of conductivity, but it requires considerable development to obtain optimal properties.
In known printed circuit board (PCB) and integrated circuit manufacture processes, the preferred means for mass manufacture is to print a circuit directly from a master article onto a suitable substrate, to create a copy of the circuit image on a suitable PCB photosensitive film, or to directly laser-write a master circuit image (or inverse pattern) onto the PCB photosensitive film. The imaged PCB photosensitive film is then used as a “mask” for imaging multiple copies onto one or more photoresist-coated substrates.
An essential feature of these methods is that the PCB photosensitive film and photoresist compositions are optimized in formulation and development so that the imaged copies are as faithful a representation of the master image as possible with respect to circuit dimensions and properties. This property is sometimes referred to as “fidelity” (or “correspondence”) and the worse the fidelity, the poorer the performance of the resulting copies. However, in mass production of these electrical circuits having designed patterns with very fine dimensional features, there are a number of compositional and operational (for example, chemical processing) conditions that naturally work against fidelity, or making faithful reproductions of the master circuit image.
This is particularly true when silver halide is used for making the multiple copies of a master circuit pattern intended for use as transparent conductive patterns. For example, development of exposed silver halide using strong developers intended to achieve high conductivity, and the high level of silver in the photosensitive coatings for the same purpose, can lead to very large dimensional differences between the master circuit image and copies made thereof using various mask elements. In addition, this lack of faithful reproduction of the dimensions in the master circuit image is strongly influenced by the dimensional scale of the circuitry images that are being reproduced. Thus, smaller features in the master circuit image become larger and the larger features in the master circuit image become smaller. These objectionable changes in the features from “master to copy” result in reduced conductivity in the resulting copy patterns and overall poorer performance in the electrical devices in which they are incorporated.
It requires considerable research and development effort to determine the various causes of the lack of fidelity between master circuit image and copies, especially when photosensitive silver halide is used for this process. There are numerous publications relating to using photosensitive silver halide in this manner, but none that addresses the noted problem.
For example, U.S. Patent Application Publication 2011/0308846 (Ichiki) describes the preparation of electrically-conductive films formed by reducing a silver halide image in electrically-conductive networks with silver wire sizes less than 10 μm, which electrically-conductive films can be used to form touch panels in displays. In addition, improvements have been proposed for providing conductive patterns using photosensitive silver salt compositions such as silver halide emulsions as described for example in U.S. Pat. No. 8,012,676 (Yoshiki et al.).
Recently designed improved electrically-conductive articles are prepared from photosensitive silver halide precursor articles as described for example in copending and commonly assigned U.S. Ser. No. 14/166,910 (noted above).
Electrically-conductive silver articles have been described for use in touch screen panels that have electrically-conductive silver grid patterns on both sides of a transparent substrate, for example as in U.S. Patent Application Publications 2011/0289771 (Kuriki) and 2011/0308846 (Ichiki).
U.S. Patent Application Publication 2014/0367620 (Gogle et al.) describes methods for enhancing the electrical conductivity of silver images provided in photosensitive silver halide elements using various post-development and fixing treatments.
While these methods provide an important advance in the art, there is a need for further improvements to maintain desired electrical conductivity.